1. Field of the Invention
This invention relates generally to the field of transfer chambers for passing objects between two differentially-pressurized environments, and, more particularly, to an improved transfer chamber for use in an orbiting space station.
2. Description of the Prior Art
It is sometimes desired to transfer an object from one environment to another environment, which is pressurized differently from the first. The first environment may, for example, be the cabin of a submerged object, and the other environment may be the surrounding liquid. Alternatively, the first environment may be a pressurized cabin of a spacecraft, and the other environment may be space. Technological developments in recent years have afforded the capability of extra-vehicular activity (EVA) from spacecraft. In this latter application, it has been deemed practical heretofore to simply provide an airlock chamber with inner and outer access doors. Since the number of egresses and ingresses through such an airlock has been somewhat limited, it has been deemed practical to simply provide the spacecraft with additional compressed air, to accommodate that which is lost when the outer door is opened to space.
However, present plans call for a permanently-orbiting space station in which the frequency of operation of such an airlock will likely be dramatically increased, and over a much greater length of time. For example, men, tools, and equipment may have to frequently passed through such airlock during the initial construction of the space station, and during its subsequent operation and repair. In such extended usage and operation, the cumulative effect of cabin air lost or vented to space when the outer door is opened, and/or the amount of energy conserved in evacuating the airlock prior to opening the outer door, may well become significant.
Upon information and belief, present plans for the space station call for the use of multi-stage pumps to partially evacuate the airlock, prior to opening to the outer door vent. However, it is not deemed practical to remove more than about 90% of the air in the airlock. Even so, due to the compressibility of air, the pump would have to be operated so as to pass a volume many times greater than the volume of the airlock. This greatly increases the size, complexity and energy requirements of the pump. Moreover, the pumping time needed to exhaust the chamber would be greatly extended, at the expense of limiting the frequency of operation and the stand-by capability of handling emergency transfers. Furthermore, while mechanical pumps must be lubricated, no liquid or vapor-producing lubricants can be used for fear of contaminating the purity of the cabin air.